(1) Field of the Invention
The invention is related to a helicopter with a cycloidal rotor system with blades disposed at a tail boom with the features of the preamble of the claim 1.
(2) Background Art
An empennage of a classical helicopter configuration features 1. a fixed horizontal stabilizer, 2. a fixed vertical fin and 3. a tail rotor.                1. The horizontal stabilizer provides static pitch attitude stability, by generating a negative lift and provides via the tail boom lever a velocity dependent positive pitch, in order to keep the fuselage in a more or less horizontal position minimizing the configuration drag but at the cost of positive lift. A first problem of this classical configuration is: Since the horizontal stabilizer incidence angle is fixed, its negative lift cannot be fully adjusted to the flight condition, keeping the fuselage in its minimum drag position. Finally, due to this problem the pilot is lacking one degree of control freedom to fully control fuselage and aircraft attitude.        2. The vertical fin provides yaw stability and generates in forward flight part or all of the antitorque for the main rotor. Again the vertical fin incidence is built in and thus fixed, resulting in a side force that cannot be freely adjusted and that is dependent on the forward flight speed of the helicopter.        3. The possibility to freely adjust said side force is provided by the tail rotor, providing all of the antitorque force in hover condition and almost no additional force in cruise. The side forces and the lift act in a vertical plane with a normal vector parallel to the tail boom. A second problem is the helicopter's limited maximum horizontal speed, since the main rotor has to provide the propulsive force. This propulsive force is naturally limited, since it depends on the rotor specific limitations in tilting the tip path plane forward.        
The document U.S. Pat. No. 2,580,428 A discloses an aircraft with cycloidal propulsion units including respectively airfoil blades pivotally mounted along an essentially horizontal blade axis parallel to the hub axis and perpendicular to a longitudinal axis of the aircraft.
The document WO 2007106137 A1 discloses a cycloidal propulsion unit for controlling a thrust vector including a hub that rotates about a hub axis. Further, the unit includes an airfoil blade pivotally mounted on the hub along a blade axis parallel to the hub axis and perpendicular to a longitudinal axis of the aircraft. As a result, the blade may pivot about the blade axis while travelling along a blade path during rotation of the hub. The unit further includes a ring that rotates around a ring axis parallel to the hub axis. The ring is interconnected with the blade via a control rod. Also, a device is engaged with the ring to selectively position the ring axis relative to the hub axis. As a result of these structures, selective positioning of the ring axis provides control of the rotation of the blade about the blade axis as the blade travels along the blade path.
The document WO 2009109918 A2 discloses a cycloidal rotor system having airfoil blades travelling along a generally non-circular, elongated and, in most embodiments, dynamically variable orbit. Such non-circular orbit provides a greater period in each revolution and an optimized relative wind along the trajectory for each blade to efficiently maximize lift when orbits are elongated horizontally, or thrust/propulsion when orbits are vertically elongated. Most embodiments, in addition to having the computer system controlled actuators to dynamically vary the blade trajectory and the angle of attack, can also have the computer system controlled actuators for dynamically varying the spatial orientation of the blades; enabling their slanting motion upward/downward and/or back sweep/forward sweep positioning to produce and precisely control a variety of aerodynamic effects suited for providing optimum performance for various operating regimes, counter wind gusts and enable the craft to move sideways and to allow roll and yaw control of the aircraft. Thus a rotor is provided, which when used in a VTOL rotorcraft, will require lower engine power to match or exceed the operating performance of VTOL rotorcrafts equipped with prior art rotors, this rotor also offers increased efficiency and decreased required power when used for generating the propulsive force for various vehicles or used as a fan.
The document JP 2009051381 A discloses a cycloidal blade capable of generating an advancing force during forward flying and accelerating forward speed, said cycloidal blade being disposed at the rear end of a tail boom of a helicopter to generate a propulsive force F in one direction. The blade includes a rotating shaft which extends along a vertical shaft of the helicopter, a plurality of blades which extend along the vertical shaft of the helicopter and rotate together with the rotating shaft, and a pitch angle change mechanism which decreases a pitch angle of the blade passing the opposite side to the one direction by moving in a direction opposite to the one direction, and increases the pitch angle of the blade passing on the same side with the one direction.
The document DE 102007009951 B3 discloses an aircraft with a closed cylinder drivable around a transverse axis of the aircraft with a controllable number of revolutions for generation of lift and/or propulsion after the Magnus effect. A radial blower having adjustable driving power is assigned to each of the cylinders for generating air flow that flows transversely against the cylinder. A wing profile of the radial blower has rotor blades that are pivotable around an aligned axis parallel to a rotation axis where a rotor of the radial blower concentrically surrounds the cylinder with a distance.
The document U.S. Pat. No. 1,761,053 discloses an airplane with a semi-cylindrical housing open upward and with a rotatable plane operable in the housing.
The document DE102008015073 A1 discloses a helicopter with a main rotor arranged on a cabin, on which a rear rotor is fixed over a rear bracket at a distance from the cabin for torque balancing. The rear bracket is provided with units for aerodynamic support for torque balancing. The devices for aerodynamic support for the torque balancing comprise a high-lift flap on the side turned away from the main rotor rotating direction extending along the rear bracket for accelerating the flow of the discharged air passing through the area of main rotor.
The document U.S. Pat. No. 4,948,068 A discloses a no tail rotor system for a helicopter. The addition of vortex generators in the longitudinal slots or nozzles, which produce the circulation control portion of the system which combines with a jet thruster and fluid resource, replaces the tail rotor.
The common disadvantage of all of said rotor systems of the state of the art is a low lift to drag ratio, limiting the efficiency of the generation of a propulsive force.